This invention relates to scanned displays. More specifically it relates to scanned displays such as are used with computer access devices, communications aids, or the like.
The field of devices which provide a user with the ability to access a computer for the purpose of controlling or determining its operation generally includes devices such as keyboards, tape readers, and punched card readers. The field of computer access devices can also include communication aids or other devices having displays made up of a plurality of display cells which are selectable by the user. One area in which communication aids are employed with great effect is that of communicative handicaps. Individuals having severe handicaps such as cerebral palsy, which reduce their abilities to communicate by the usual modes of expression such as speech and writing, must use aids to make their communications intelligible. A class of communication aids for the handicapped comprises an aid which enables a user to communicate by employing any volitional means at his disposal to select from a displayed array of communication elements. Communication aids of this class are described in G. C. Vanderheiden, et al., ed., Nonvocal Communication Resource Book, University Park Press, 1978, and in G. C. Vanderheiden, et al., ed. Nonvocal Communication Techniques and Aids For The Severely Physically Handicapped, University Park Press, 1975.
One such communication aid includes a display panel divided into a two-dimensional matrix of individual display cells, with each cell containing a character such as a symbol, letter, or numeral. The user communicates by selecting a single cell, or group of cells.
One technique of cell selection provides a visible, mobile indicator which moves from cell to cell, and is stopped by the user when it indicates a cell he wishes to select. An instrument embodying this technique is the Model 100 communication system, manufactured by Zygo Industries, Incorporated, Portland, Ore. In one form of this technique, indication consists of optically activating a cell by producing or intensifying illumination associated with the cell. For example, the cell may be optically activated by illuminating a visible light source, such as a light-emitting diode (hereinafter, LED) which is contained in the cell. The communication aid has circuitry which optically activates the cells in a systematic manner. When a cell which a user wishes to select is activated, he closes a switch to interrupt the activation, which causes the cell's LED to remain illuminated. The systematic activation is resumed either automatically, or manually by another switch closure. This technique of selection is very effective for individuals having healthy cognitive abilities but few volitional actions, because its use depends only upon switch closures which can be accomplished by, for example, the moving of a digit, movement of a limb, eye motion, or an uttered sound.
As is known in the art, a communication aid can be provided with encoding circuitry, which will produce a coded signal corresponding to the character contained in the selected cell. The coding circuitry can be interconnected with a computer system, which includes a printer or display, and which can respond to the coded signals by printing or displaying the character. This enables the user to compile selected characters into verbal communications such as sentences.
It is evident that such a communication aid can be utilized in a more sophisticated manner. For example, appropriate computer control commands can be provided in selected display cells to allow any user, handicapped or not, to write or execute computer programs. In short, the aid can functionally correspond to a manual computer keyboard.
The user of such a device may be assisted in selecting a display cell by the provision of electric circuitry to control and implement the optical activation of an array of display cells according to a scanning technique, a number of which are described in the Vanderheiden, et al., reference cited above. A scanning technique comprises at least one systematic manner or "mode" of scanning which includes a plurality of scan transitions, with each scan transition including the successive activation of at least a related pair of display cells.
In fact, most of the well-known scanning techniques used to activate the display cells of a display panel comprise more than one scanning mode. For example, communication aids which operate by means of multi-mode scanning techniques are known to be provided with electrical control devices, such as switches or "joysticks," which enable the user to change the operation of the aid from one scanning mode to another.
One multi-mode scanning technique known in the art is the row-column scanning technique. The cells of a display panel may be arranged into a regular two-dimensional matrix, whereby they will naturally form rows and columns. In the row-column scanning technique, all of the cells in one row are optically activated simultaneously, and then extinguished simultaneously, while the next row is activated, and so on. In this mode of operation the communication aid is said to be "row scanning", the movement of optical activation from one row to another is termed a "row scan transition," and the time consumed during a row scan transition is called the "row scan transition time." It is most often the case that all of the row scan transition times are equal.
When a row containing the cell which the user wishes to select is activated, he closes the switch to select the row, and, in selecting it, causes the scanning operation to change to a mode wherein individual cells in the selected row are successively optically activated, one at a time. This is called the "column scanning" mode, wherein the movement of optical activation from cell to cell is termed a "column scan transition," the duration of which is termed the "column scan transition time." It is most often the case that the row and column scan transition times are equal.
When, in the column scanning mode, the cell containing the character which the user wishes to select is optically activated, the user closes the switch to select the cell. In what may be termed the "confirmation" mode of operation, scanning ceases while the selected cell remains optically activated. In most scanned displays having this mode, row scanning is automatically resumed after the selected cell has remained optically activated for a period of time.
It is known that both the row and column scanning modes are cyclic, in that, if all rows in the row mode or all cells in the column mode are scanned without the user making a selection, the aid will be rescanned in the respective mode until a selection is made. Thus, should the user, because of inattention or slow reflexes, miss a selection during a first scan cycle, he will have an opportunity to make his selection during a succeeding scan cycle in the then-current scanning mode.
The Applicants have observed that, while the mean time required by an individual user to react to a scan transition and make a selection by switch closure (termed "mean selection reaction time") may shorten with practice, the user's selection reaction time invariably lengthens in reaction to a change in scanning mode. For example, upon selection of a row during the row scanning mode, the mode changes to a column scan, and immediately following the mode change, there is a perceptible time (called "adjustment time" herein), which varies from user to user, during which the user must first adjust his reactive faculties to the change in scanning mode before his instantaneous selection reaction time shortens to equal his mean selection reaction time. The Applicants have observed that the adjustment time has a short persistence and appears to decay over a time period measured from the change in mode. The user's adjustment time may interfere with his ability to react to the first few row or cell transitions with the same speed that he can react to later transitions. The result can be that the user can miss the first opportunity to select a row or cell if it occurs soon after a change of scanning mode. Then, the user has to await a subsequent cycle to make the missed selection, which can reduce his overall communication speed.
Stated differently, there is a measurable time after a change of scanning mode during which the cognitive and reactive faculties of a user adjust to the change. This adjustment time may cause a user to miss the first opportunity to make a selection and force him to await a whole scan cycle before he again has an opportunity to select.
This adjustment time is evidenced also in other multi-mode scanning techniques wherein a change is made in the mode of scanning an array of display cells to assist the user to quickly select a desired cell.
The Applicants have attempted to adapt various multi-mode scanning techniques to account for a user's adjustment time by lengthening the first scan transition occurring after a change in scanning mode. This has not succeeded, possibly because the adjustment time is a complex function related both to a change in scanning mode and to a change in scan transition time. The Applicants have found that this approach does not perceptibly improve the efficiency with which a scanned display is used because a significant number of first selection opportunities are still missed immediately after the abrupt change in scan transition time.
Accordingly, in display devices utilizing a multi-mode scanning technique to select from a plurality of display cells, there exists a need to adapt the technique to account for the time required by the user to adjust to a change in scanning mode so as to increase the possibility that a desired selection can be made immediately after a change in the mode.